1. Field of the Invention
The present invention relates to a data processing apparatus employing virtual storage system, and more particularly to an address translation system in which the real address is longer than the logical address.
2. Description of the Prior Art
In general, a large-capacity data processing apparatus adopts a virtual storage system. Namely, users' programs or data are stored in the continuous regions on a virtual memory and a main memory is independently supervised, whereby logically continuous addresses are relocated at arbitrary addresses in the main memory so as to effectively utilize the main memory. In this case, logical addresses are alloted to the programs and data stored in the virtual memory while real addresses obtained through translation by an address translation mechanism are used for the addressing of the main memory.
The address translation mechanism of the virtual storage system is used to support the virtual memory, that is, to make it possible to process programs and data too large for the capacity of the main memory in accordance with instructions.
The recent progress of the hardware techniques of memories has produced a small-sized, very large capacity memory which could not be even expected in the past. In the meanwhile, the development of programs which are the essence of software was rapidly carried out until the package of the available programs became enormous. However, the address space, i.e., logical address spaces, for the programs are restricted by the established architecture so that it requires a considerable amount of money and labor to change the already arranged architecture. Therefore, when in correspondence with the advance of software techniques, it is intended to adopt a memory device of such a large capacity as not being covered by the conventional architecture, the adoption must be effected in a manner capable of ensuring the use of the conventional programs.